Development is underway of a sensor network including networked sensor nodes which are small integrated units of a sensor, a wireless apparatus, and a data processing function. Desirably, such sensor nodes are battery-less and capable of generating electric power on their own. Thus, adoption of an ultra-small sized system for micro-power generation is being considered that utilizes the in-situ environment, such as a solar battery system, a thermoelectric generation system, or a vibrating power generation system.
As a type of micro-power generation technology, micro-piezoelectric power generation that utilizes a piezoelectric phenomenon is known. Micro-piezoelectric power generation is a system for converting mechanical force, such as vibrations or shocks, into electric energy. The micro-piezoelectric power generation technology may be widely applied for various applications including human bodies, living organisms, and other moving objects, in addition to cars and machines.
While various types of micro-piezoelectric power generation have been studied and researched, a basic type has a unimorph structure based on a combination of a vibrating plate and a weight.
A unimorph structure is known in which a piezoelectric capacitor is mounted on a cantilever with a tip-shaped weight attached to the end of the cantilever. In this structure, stress is applied to the cantilever and the piezoelectric capacitor due to the up-down movement of the weight. The piezoelectric capacitor may have a structure including a laminate of a platinum lower electrode, a PZT film, and an aluminum upper electrode.
However, in the unimorph structure in which a piezoelectric capacitor is formed on the cantilever, the ratio of volume of the piezoelectric element to the entire volume of the piezoelectric generating apparatus is small, so that the power generating efficiency is low.